1. Field of the Invention
The present invention relates to an electromagnetic actuator which has no adverse effect on adjacent electronic equipments and electromagnetic members.
2. Background Art
In the past, several structures have been proposed as electromagnetic actuators adapted to maintain attracting force due to permanent magnets.
One example of such electromagnetic actuators includes a stator 1 and a movable body 2 as shown in FIG. 38, in which the stator 1 and movable body 2 are arranged symmetrically about the axis of symmetry and constitute together a magnetic circuit having a substantially E-shaped cross section. In two spaces included in the E-shaped structure, coils 31, 32 are provided respectively, and a magnetized permanent magnet 15 is provided at a projecting portion 14 which is projected along a central line of the structure (e.g., see Patent Document 1).
In FIG. 38, since the width of a first gap 41 is less than the width of a second gap 42, the magnetic flux produced by the permanent magnet 15 flows more in the magnetic circuit including the first gap 41. Thus, magnetic attracting force to be applied leftward is generated in the movable body 2, thereby fixing the movable body 2 at a leftward latched position. When the latched state is released, an electric current is caused to flow in the coils 31, 32 to reduce the magnetic flux in the first gap 41 while increasing the magnetic flux in the second gap 42, thereby generating driving force to move the movable body 2 leftward.
Another electromagnetic actuator, as shown in FIG. 39, includes a coil 3, a movable body 2 adapted to move on the central axis of the coil 3, and a stator 1 provided to cover the top and bottom faces and outer periphery of the coil 3. In addition, a permanent magnet 15 is disposed in a gap surrounded by the stator 1 and the movable body 2, whereby the movable body 2 can be attracted to the stator 1 due to the magnetic field to be generated by the permanent magnetic 15 (e.g., see Patent Document 2).
In FIG. 39, when the latched state is released, an electric current is caused to flow in the coil 3 to reduce the magnetic flux from the permanent magnet 15. Thus, the attracting force downwardly applied to the movable body 2 is reduced, thereby releasing the latched state. Accordingly, the movable body 2 rises due to a load.
Patent Document 1: TOKUKAIHEI No. 7-37461, KOHO
Patent Document 2: TOKUKAI No. 2002-289430, KOHO
In the electromagnetic actuator described in the Patent Document 1, since the permanent magnet 15 is provided in the magnetic circuit path to be created by the coils 31, 32, the permanent magnet 15 is directly and inversely excited upon releasing the latched state, leading to demagnetization.
In the electromagnetic actuator described in the Patent Document 2, the magnetic flux to be generated from the permanent magnet 15 may tend to leak outside, thus having an adverse effect on adjacent electronic equipments and electromagnetic members.
Generally, the electromagnetic actuator is required to be highly efficient, thus there is a need for reducing the current to be used upon operation as much as possible.